1. Field of the Invention
This invention relates to a driving circuit arranged to drive a vibratory-wave motor.
2. Description of the Related Art
Heretofore, there have been proposed many cameras of the kind using a vibratory-wave motor for driving a lens. The cameras of this kind include some arrangement for allowing the photographer to manually drive the lens in addition to an electrical driving arrangement for driving the lens by the power of the vibratory-wave motor.
The known methods for the above-stated manual lens driving arrangement include, for example, a method disclosed in Japanese Patent Application Laid-Open No. SHO 59-101608. According to this method, a stationary vibratory wave is generated by electro-mechanical energy converting means to bring frictional contact between a stationary body and a vibrating body into a kinetic state of friction during the manual lens driving process. This method reduces not only the coefficient of friction but also the area of contact, and thus permits the manual lens driving operation to be lightly accomplished without necessitating any complex structural arrangement.
However, the above-stated conventional manual driving method does not enable the photographer to directly select and change the rotating torque of the lens during the manual operation. Besides, in accordance with this method, a stationary wave must be constantly generated. Therefore, this method necessitates an incessant current flow even while the lens is not rotated. This increases electric energy consumption. It has been another problem with the prior art method that, in order to make the rotating torque of the lens variable, the camera must have some additional rotation torque changing means connected to the vibratory-wave motor.